Refining fuel oil to render the overall property thereof better so as to obtain, for example, fuel oil having higher combustion efficiency and less likely to contaminate the environment is the goal which the fuel manufacturing industry endeavors to achieve.
For instance, US 2013/0206642 A1 discloses a method for processing heavy oil, which comprises the following steps: (1) conducting a solvent deasphalting process using a heavy oil feedstock as feed with an extraction solvent in an extraction tower, and collecting de-asphalted oil and a de-oiled asphalt phase including the extraction solvent; (2) entering the de-oiled asphalt phase including the extraction solvent into a thermal cracking reactor after mixing the same with a dispersing solvent to conduct a thermal cracking process, so as to obtain a thermal cracking reaction product and coke; (3) leading out the thermal cracking reaction product, and separating therefrom the solvent, thermal cracking oil, and heavy gas oil; and (4) mixing the de-asphalted oil and the thermal cracking oil separated from the thermal cracking reaction product to obtain upgraded oil. In step (1), the extraction solvent used in the solvent deasphalting process is C3-C6 alkane, and the temperature and pressure of the extraction tower are respectively in the range of 80° C. to 250° C. and the range of 3.5 MPa to 10 MPa. The solvent deasphalting process serves to enable the extraction solvent to be in the supercritical fluid state, so that the asphalt phase in the heavy oil feedstock, which is a heavy component, and the carbon number of the hydrocarbon of which is not less than 33, can be extracted.
Furthermore, CN 105567319 B discloses a method for processing heavy oil, which comprises the following steps: subjecting heavy oil to a solvent deasphalting process in an extraction equipment, so as to obtain de-asphalted oil and de-oiled asphalt; and sequentially subjecting the de-oiled asphalt obtained to a hydrogenation process and a fractionation process, so as to convert the asphalt in the heavy oil to more valuable light oil. The extraction solvent used in the solvent deasphalting process is a C3-C5 hydrocarbon, and the temperature and pressure of the extraction equipment are respectively in the range of 50° C. to 90° C. and the range of 2 MPa to 4.5 MPa. The solvent deasphalting process serves to enable the extraction solvent to be in the supercritical fluid state, so that the asphalt in the heavy oil, the carbon number of the hydrocarbon of which is not less than 33, can be extracted.
In addition, US 2010/0032342 A1 discloses a method for re-refining lubricating oil. Specifically, a propane extraction process and a hydro-fining process are used in combination to recover and reuse waste lubricating oil. The propane extraction process is able to remove the asphalt, resin, additives, and metal compounds in the waste oil and to recover base oil fraction. The re-refining method comprises the following steps: (1) filtering waste lubricating oil through a multi-layer filter; (2) processing the waste lubricating oil in a cyclone separator to remove water from the waste lubricating oil after the waste lubricating oil has been filtered; (3) distilling the waste lubricating oil from the cyclone separator at 200° C. to 220° C. and −101.1 kPa in a flash tower to eliminate the trace amount of water and light hydrocarbon fraction in the waste lubricating oil; (4) introducing liquefied propane into the waste lubricating oil from the flash tower to form an oil/propane mixture, and heating the oil/propane mixture to 80° C. to 90° C.; (5) processing the oil/propane mixture through an extraction tower to perform sedimentation of the asphalt, resin, additives, and metal compounds from the oil; and (6) transferring the oil/propane mixture from the extraction tower to a propane recovery tower where propane is recovered from the mixture and the waste lubricating oil is ready for further processing. Generally speaking, lubricating oil contains a heavy hydrocarbon fraction, the carbon number of the hydrocarbon of which is not less than 33. Since liquefied propane is introduced to be mixed with the oil and the oil/propane mixture is heated to 80° C. to 90° C. in step (4), the propane can reach the supercritical fluid state upon the extraction.
In view of the foregoing, refinement of highly viscous fuel oil is complicated and costly due to the need of a supercritical fluid during extraction. Therefore, it is necessary to develop a cost-effective method for modifying or refining fuel oil having a high viscosity and a low flowability.